The synthesis of an oxygen-bridged hydroxy[15]annulenone: the effects of introducing one hydroxy group into the flexible segment of a 14π perimeter

Abstract

Mono-trans-hydroxy[15]annulenone (6) forms a keto-enol tautomeric mixture with the keto tautomer (7) in CH₂Cl₂; (6) was rapidly isomerized into the cis-enol (8) on dissolution in dimethylformamide, dimethyl sulphoxide, and MeOH, indicating that the intramolecular H-bond of (6) is easily broken owing to the motional freedom of the segment on which the OH group was introduced.